The Democratic Party presidential primary in Indiana took place just days after the U.S. Supreme Court ruled that states can require voters to produce photo identification without violating their constitutional rights.

By a margin of six-to-three, the court last week upheld a state law enacted in 2005 that required voters to produce government-issued identification at the polls.

The state's Republican-led legislature passed the bill along party lines, saying it would reduce voter fraud. Democrats and other critics said the law could keep some minorities, poor people, the elderly and other traditional Democratic supporters from voting in the November presidential election.

Indiana was one of several states that enacted voter identification laws following the disputed presidential election in 2000 in which Republican George Bush defeated then-Democratic Vice President Al Gore following a lengthy battle over votes in Florida.

Nearly half of all U.S. states require some form of identification at the polls. One exception is Missouri, where the state supreme court ruled in 2006 that a similar voter ID law was unconstitutional.